Chlorofluorocarbons (CFCs) are synthetic chemical compounds widely used in refrigeration and air conditioning; as aerosol propellants and solvents; in forming foams, including those used in fast-food packaging; and in rigid insulation. Scientists now see these synthetic chemicals as the main threat to Earth's protective ozone layer. Because CFCs are immune to destruction in the troposphere, and because they eventually float upwardly, their manufacture and release have lead to the accumulation of large amounts in the stratosphere. In the stratosphere, CFCs are broken down by sunlight into chlorine, which has a catalytic and destructive effect on ozone. The result has been a significant decline in the global ozone shield and an increase in the amount of harmful ultraviolet radiation reaching the surface of Earth. According to a United Nations' study, every 1 percent drop in ozone will lead to a 3 percent increase in non-melanoma skin cancers in light-skinned people, as well as dramatic increases in cataracts, lethal melanoma cancers, and damage to the human immune system. Higher levels of UV light may also worsen ground-level pollution and hurt plants, animals, and especially light sensitive aquatic organisms.
As a result, destruction of CFCs, and in some instances, reclamation of CFC refrigerants is a vital component of the national and global strategies for protection of the earth's ozone layer in a manner consistent with minimal economic disruptions associated with the phase-out of this class of chemicals. There are still sizable reserves of CFCs on hand which must be treated and converted to environmentally benign substances. Likewise, until existing refrigeration and air conditioning equipment is replaced or retrofitted with devices which are capable of operating with more environmentally friendly refrigerants, as CFC production is curtailed and eventually eliminated, industry and consumers must rely increasingly on the availability of reclaimed refrigerants.
However, successful reclamation is presently hampered due to the occurrence of inadvertent contamination of refrigerants by other refrigerants. In order to qualify for reuse, reclaimed refrigerants are required to meet the American Refrigeration Institute's "700" specifications which stipulate the permissible levels of contaminants. That is, strict limits are placed on moisture, particulates, acidity, oil content, non-condensible gases, and other refrigerants present. Existing refrigeration and air conditioning equipment appears capable of employing reclaimed refrigerants. Existing reclamation processes are capable of meeting all of the foregoing criteria with the exception of "other refrigerants", which are not permitted to exceed 0.5 percent maximum.
One example of a widely found refrigerant mixture is Freon.RTM. 12, a trademark of E. I. DuPont, which is dichlorodifluoromethane, contaminated with Freon 22, which is chlorodifluoromethane, hereinafter called R-12 and R-22, respectively. Although removal of the unwanted R-22 contaminant from such a mixture would appear to be readily accomplished by distillation due to differences in their boiling points (R-12 b.p. -29.8.degree. C. and R-22 b.p. -41.degree. C.), separation by distillation is not readily achieved due to the formation of an azeotrope consisting of 75 percent R-22, when the two refrigerants become mixed.
Other known technologies for the destruction of CFCs such as thermal oxidation, catalytic decomposition, supercritical water oxidation, plasma destruction methods, biological processes, UV photolysis, and so on, are either in experimental stages of development, economically unattractive or incapable of selectively destroying the unwanted contaminating refrigerant without also eliminating the desired refrigerant.
Useful methods for purification of refrigerant mixtures have been disclosed in copending application Ser. Nos. 207,286 and 207,289 filed Mar. 7, 1994. Such methods are especially useful in reclamation processes where production of certain CFCs, such as R-12 are being phased-out of production, but market demand remains strong. While such methods provide efficient and economic means for selectively purifying refrigerant compositions comprising two or more refrigerants without eliminating the desired refrigerant, the methods usually result in the dehalogenation and destruction of at least one of the refrigerants, i.e., the contaminating refrigerant, such as R-22.
Accordingly, it would be desirable to have alternative methods for efficient purification of refrigerants in short supply or which are being phased out of production, but which have become contaminated with other refrigerants. Such methods of purification should enable the separation and recovery of refrigerants without chemical destruction of potentially useful other refrigerants.